Rare earth and zirconium oxide materials are critical for a broad range of technologies. Important industrial sectors such as defense, manufacturing, energy, transportation, optics and electronics all utilize rare earth materials in abundance. Rare earths exist as integral components in many technologies, including navigation/guidance systems, petroleum refining catalysts, advanced vehicle batteries, wind turbine motors, jet engines, miniature disk drives, speakers, televisions and monitors, compact fluorescent light bulbs and optical cables. Additionally, there are currently a limited number of economically viable sources of rare earths, making the recycling of rare earths an invaluable practice to industry. However, only a small percent of all rare earth minerals are recycled. The disclosed embodiments provide a simple method for the recycling of oxide materials that is especially suited for rare earth containing materials and zirconia containing materials.
Disclosed in embodiments herein is a method for recovery, in reusable form, of rare earth minerals from waste materials containing rare earth minerals and zirconia. Such waste materials may be produced by a number of industrial processes, including thermal spray coating, electron beam vapor deposition, green machining of dental materials, and cubic zirconium gem production. The basics of this method consist of the following: a) mixing an ammonium sulfate powder and a powder containing oxide waste material; b) firing the mixture at a temperature sufficient to decompose a waste residue, which is, to a large degree, soluble in aqueous solution; c) dissolving the residue in water to obtain a solution that includes rare earth constituents in salt form; d) separating rare earth constituents from the solution using at least one separation method; and e) subsequently using the separated rare earth constituent (salt or solution) as a raw material. If these waste materials occur in coatings, the coatings are removed by treating the material in a concentrated ammonium sulfate solution to cover the surface, and then heating the coated part to allow the ammonium sulfate to preferentially digest and disrupt the coating. The zirconia may be further recovered from the waste filtrate in (d) via precipitation or other separation methods. The reactants used in the recovery may also be recovered by appropriate precipitation and concentration of the filtrate produced in (d).
Further disclosed in embodiments herein is a method for recovery, in reusable form, of rare earth minerals from waste materials containing rare earth minerals but no zirconia. Such waste materials are produced by compact fluorescent light bulbs, rare earth containing catalysts, rare earth-iron alloy magnets, lanthanum manganate fuel cell electrodes, and NiMH batteries. If such materials occur in coatings, a method is also disclosed for removal of the coatings containing these wastes. The steps involved are the same as above pertaining to the reactions to which the materials are subjected, except that an oxalate precipitation agent is used to precipitate the rare earth minerals in (d) in the absence of zirconia. Additionally, if the rare earth waste materials are non-oxides, the materials must be oxidized prior to reaction with ammonium sulfate. If such materials occur in coatings, the materials are treated in a saturated ammonium sulfate solution to coat the surface with ammonium sulfate, which allows for a preferential chemical attack on the coated surface to effect removal of the materials.
Also disclosed herein is a method for the recovery of zirconia from zircon, which is a typical waste produced by metal casting operations.
The various embodiments described herein are not intended to limit the disclosure to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the various embodiments, examples and equivalents set forth. For a general understanding, reference is made to the drawings. In the drawings, like references have been used throughout to designate identical or similar elements. It is also noted that the drawings may not have been drawn to scale and that certain regions may have been purposely drawn disproportionately so that the features and aspects could be properly depicted.